The present invention relates to a venous catheter, comprising a flexible and resilient tube of synthetic polymer, such as silicone rubber, a terminal section of which is adapted to be inserted into the superior or inferior vena cava, in such a manner to place a free end of the terminal section at, or close to the cavo-atrial junction in order to introduce a liquid into the blood cycle.
Venous catheters of silicone rubber or other synthetic polymers are used to carry out intravenous extended perfusions, for instance for parenteral feeding purposes. These catheters are inserted into the venous systems for the treatment of ascites. In these systems a perforated tubular flexible probe, made of synthetic polymer, which is to be placed in the peritoneal cavity to drain the ascitic fluid, is connected to the catheter through a check valve. The end part of the catheter is to be inserted in the superior vena cava where the ascitic liquid will be discharged.
These shunting systems are known, for instance, from U.S. Pat. No. 3,910,283 and their application is becoming more and more widespread. Their implantation and other features are described in various publications, such as Le Veen, H. H., Christoudias, G., Ip, M., Luft, R., Falk, G., Crosbery, S., "Peritoneo-venous shunting for ascites", Ann. Surg., 180, 1974, 580-591 and Le Veen, H. H., Wapnick S., "Operative details of continuous peritoneo-venous shunt for ascites", Bulletin de la Societe Internationale de Chirurgie, 6, 1974, 579-582.
In these known systems the whole catheter is made of silicone rubber, although the use of other biologically inert, synthetic polymers is not excluded. They have frequently caused the severe disadvantage of short-term occlusion of the catheter due to the formation of deposits or thrombi. This disadvantage is linked to various factors connected to the presence of calcium ions in the blood, to the properties of the ascitic fluid and the mechanic and biochemical characteristics of the catheter of polymer.
Particularly in the case of cirrhotic ascites the ascitic liquid is rich of procoagulant factors which encourage the formation of thrombi. It has however been established that, as the ascitic liquid is drained, the formation of occlusions due to thrombi does not decrease. Probably this is due to the fact that the outlet opening of the catheter has a rather sharp edge, and the catheter, comprising a flexible and elastic tube, oscillates in the vein in synchronism with the blood pulsations and the heart beat, thus causing lesions to the wall of the vein, with the consequent formation (which has been proven) of parietal thrombi.
The same severe disadvantages occur with catheters used for intravenous perfusions. These catheters, especially in the case of parenteral feeding, are subject to occlusions within two or three days from the implantation, whereas they would be required to function for periods of one or more months.
The object of the present invention is to provide a venous catheter with a negligible risk of occlusions compared to the known catheters.